Many older adults face impaired hand motor function, apart from arthritis, that affects their ability to grasp and manipulate objects. These declining motor abilities impede the capacity to perform daily living skills or pursue hobbies. Recent research indicates that the control of fingertip forces for dexterous grasp depends upon sensory information, sensory-motor integrative processes, and memory. Dysfunctions of these systems in older adults are common and may contribute to impaired dexterity by altering the fingertip forces for grasp. However, little research has been directed along these lines. The long-term objectives of this project are to: 1) Determine mechanisms that contribute to impaired prehension in old age; and, 2) Identify ways to ameliorate the functional impact of those mechanisms. The present proposal addresses the first of these goals by examining the effects of aging on the fingertip forces used during grasp. Hypotheses focus on possible mechanisms for altered fingertip forces in old age. Feasible mechanisms include; diminished peripheral sensory signals, impaired sensory-motor integration, and exceedingly variable muscle forces within an individual. The fingertip forces that old and young adults use to grasp and manipulate objects will be recorded while they grip and manipulate instrumented test objects. The ability of older adults to use sensory information to control fingertip forces will be studied by examining motor responses to slips of a grasped object, by subjecting a grasped object to unexpected pulling loads, and by surreptitiously varying the weight and friction of a test object that is grasped and lifted. However, these experiments alone cannot determine if changes in force control are due to faulty peripheral sensory input or an impaired ability to use the sensory information. Therefore, the effects of mild-to-moderate anesthesia of the hand on fingertip force control will be studied in young adults by experimental compression of the median nerve. Other studies will address directly if older adults suffer from impaired sensory-motor integration in grasp force control by examining their ability to use explicit visual and tactile information about object weight and friction to scale their grip force commands. Finally, reports that motor output in older adults is highly variable prompts studies on the variability of grip forces during manipulation and pinch tasks.